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Tropical Depression Fourteen Forecast Discussion Number 3
2018-10-07 10:52:09| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sun Oct 07 2018 000 WTNT44 KNHC 070851 TCDAT4 Tropical Depression Fourteen Discussion Number 3 NWS National Hurricane Center Miami FL AL142018 400 AM CDT Sun Oct 07 2018 Radar data from Belize and infrared satellite imagery indicate that the low pressure system centered just off the coast of the Yucatan Peninsula has continued to become better organized, with deep convection consolidating just to the northeast of the low-level center. Dvorak estimates have increased to T2.0 from TAFB and T1.5 from SAB, indicating that the convective pattern has become sufficiently organized for the low to now be declared a tropical depression. The maximum winds are estimated to be 30 kt based on earlier ASCAT data. The Belize radar data was extremely helpful in locating the depression's center, and the system's 12-hour average motion is north-northwestward, or 340 degrees, at a very slow 3 kt. The depression is expected to move generally northward during the next 3 days, gradually gaining speed as it enters the southerly flow between high pressure over the western Atlantic and an advancing deep-layer trough over the western half of the United States. After day 3, the trough is expected to cause the cyclone to turn northeastward and accelerate further across the southeastern United States. While the track models agree on the general scenario, there are some speed differences, most notably with the ECMWF model being slower than the other guidance. Also, the ECMWF and GFS models are located along the western edge of the guidance envelope. In light of these facts, the new NHC prediction is just a little slower than the previous one, and it lies to the west of the TVCN multi-model consensus and the HCCA model during the first 3 days of the forecast. The depression is still being hampered by 20-30 kt of westerly shear, however it is also located in an environment of upper-level diffluence to the southeast of a stationary trough over the Gulf of Mexico. The shear in the immediate vicinity of the cyclone is forecast to gradually abate during the next 2-3 days while the diffluent upper-air pattern continues, and along with sufficiently warm waters of 28-30 degrees Celsius, all indications are that the depression will gradually strengthen while it moves northward over the Gulf of Mexico. In fact, nearly every piece of intensity guidance brings the cyclone to hurricane strength before it reaches land, including the GFS, ECMWF, and UKMET global models, which all show significant deepening of the central pressure. The updated NHC intensity forecast generally lies between the ICON intensity consensus and the HCCA model for the entire forecast period, and it now explicitly shows the cyclone reaching hurricane strength by 72 hours. Key Messages for Tropical Depression Fourteen: 1. The depression is producing heavy rainfall and flash flooding over portions of Central America, and these rains will spread over western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. 2. The depression is forecast to become a tropical storm later today, and tropical storm conditions are expected by tonight over portions of western Cuba and the northeastern Yucatan Peninsula, where tropical storm warnings are in effect. 3. Storm surge, rainfall, and wind impacts are possible over portions of the northern Gulf Coast by mid-week, although it is too soon to specify the exact location and magnitude of these impacts. Residents in these areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 18.6N 86.9W 30 KT 35 MPH 12H 07/1800Z 19.4N 86.7W 35 KT 40 MPH 24H 08/0600Z 20.8N 86.4W 45 KT 50 MPH 36H 08/1800Z 22.3N 86.6W 50 KT 60 MPH 48H 09/0600Z 23.9N 87.1W 55 KT 65 MPH 72H 10/0600Z 27.6N 87.3W 65 KT 75 MPH 96H 11/0600Z 32.0N 84.0W 45 KT 50 MPH...INLAND 120H 12/0600Z 37.0N 76.0W 45 KT 50 MPH...NEAR THE VA COAST $$ Forecaster Berg
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